Only edition of this work on the sources of the prayers, the dates of their compilation and composition by R. Zev Yawitz. Mekor ha-Berakhot is on all parts of the siddur and its development. There are Hebrew and German introductions, the latter printed at both ends of the book. In the introduction R. Yawitz that this book is only an entryway to knowledge of the Ashkenaz prayer book according to the Polish rite. In the future he hopes to bring out a larger more detailed work, Avodah she-be-Lev, although it would appear that only this work was published. Mekor ha-Berakhot addresses the words and sayings in a concise manner, contending that the entire siddur, from beginning to end, is not original but rather is a compendium of from the Bible or midrashim, as demonstrated in the book. R. Yawitz also addresses the intent of the siddur in arousing the heart in prayer and the importance of knowing the sources and purposes of blessings and prayers. It is based on the the Ashkenaz Polish rite because that is the most wide spread and, according to R. Yawitz, is more pure than the Sephardic rite.

R. Zev (Wolf) ben Sussman Yawitz (1747-1924) was born in Kolno, made aliyah to Erez Israel in 1927, and died in London.